Packard, Norman H. “Intrinsic adaptation in a simple model for evolution.” In Langton, C.G. Artificial Life: Proceedings of an Interdisciplinary Workshop on the Synthesis and Simulation of Living Systems. Avalon Publishing, 141-156 (1989).
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A distinction is made between extrinsic adaptation, where evolution is
governed by a specified fitness function, and intrinsic adaptation, whicre
evolution occurs “automatically” as a result of the dynamics of a system
caused by the evolution of many interacting subsystems. A simple model
is presented to illustrate intrinsic adaptation, and the dynamics of the
population is observed through simulation of the model. The population
density over the space of genes for the model organisms may be interpreted
as an a posteriori fitness function, and is seen to undergo complex dynamics
that depend on the environment.